Reverse battery protection for battery-powered devices

ABSTRACT

Reverse battery protection circuits for devices powered by batteries coupled in parallel can include both P-channel and N-channel MOSFETs. Each positive battery terminal connector of a battery-powered device can be coupled to a gate of an N-channel MOSFET or to both a gate of an N-channel MOSFET and a gate of a P-channel MOSFET. In some embodiments, each negative battery terminal connector of the device can be connected to a gate of a P-channel MOSFET. In the event of a reverse battery connection, one or more of the protection circuit&#39;s P-channel and N-channel MOSFETS can switch to a non-conductive state to isolate the device&#39;s load from an incorrectly installed battery and prevent the incorrectly installed battery and/or other parallel-coupled battery from prematurely discharging. Methods of protecting a load from a reverse battery connection are also provided, as are other aspects.

FIELD

The invention relates generally to battery-powered devices, and moreparticularly to devices powered by batteries coupled in parallel.

BACKGROUND

Coupling batteries in parallel is a common method of providing morepower to a load. For example, some known portable blood glucose metersrequire two batteries coupled in parallel to power the meter's load(e.g., electronics). Accidental reverse battery installation in suchdevices can cause one or more problems including abnormal deviceoperation, damage to the device's load, and/or premature batterydischarge. Some devices employ mechanical safeguards, such as, e.g.,special battery connectors, to prevent inadvertent reverse batteryinstallation. However, mechanical safeguards can be expensive and/or maynot be effective with certain kinds of batteries, such as, e.g., coin orlithium cell type batteries. Some devices employ circuitry to protectagainst reverse battery installation. However, some known protectioncircuits, such as those using diodes, can result in undesirable powerlosses. Other known protection circuits, such as those using MOSFETs(metal-oxide-semiconductor-field-effect-transistors), may not beeffective in devices powered by parallel-coupled batteries. Inparticular, the type of batteries and/or the type of parallel-batteryholders and/or connectors used in a device can render some known MOSFETprotection circuits ineffective. Thus, a need still exists to providereverse battery protection for devices powered by batteries coupled inparallel.

SUMMARY

According to one aspect, a reverse battery protection circuit isprovided. The reverse battery protection circuit comprises a first loadterminal, a second load terminal, a first P-channel MOSFET having adrain, a gate, and a source coupled to the first load terminal, a firstN-channel MOSFET having a drain, a gate, and a source coupled to thesecond load terminal, a first positive battery terminal connectorcoupled to the drain of the first P-channel MOSFET and to the gate ofthe first N-channel MOSFET, the first positive battery terminalconnector configured to electrically connect to a first batteryterminal, and a first negative battery terminal connector coupled to thedrain of the first N-channel MOSFET and to the gate of the firstP-channel MOSFET, the first negative battery terminal connectorconfigured to electrically connect to a second battery terminal.

According to another aspect, a reverse battery protection circuit isprovided that comprises a first P-channel MOSFET having a gate, a drain,and a source; a second P-channel MOSFET having a gate, a drain coupledto the gate of the first P-channel MOSFET, and a source coupled to thesource of the first P-channel MOSFET; a first N-channel MOSFET having agate coupled to the gate of the second P-channel MOSFET, a drain coupledto the drain of the second P-channel MOSFET and to the gate of the firstP-channel MOSFET, and a source; a first load terminal coupled to thedrain of the first P-channel MOSFET; a first positive battery terminalconnector coupled to the source of the first P-channel MOSFET and to thesource of the second P-channel MOSFET, the first positive batteryterminal connector configured to electrically connect to a first batteryterminal; a second positive battery terminal connector coupled to thegate of the first N-channel MOSFET and to the gate of the secondP-channel MOSFET, the second positive battery terminal connectorconfigured to electrically connect to a second battery terminal; a firstnegative battery terminal connector configured to electrically connectto a third battery terminal; a second negative battery terminalconnector configured to electrically connect to a fourth batteryterminal; and a second load terminal; wherein the first negative batteryterminal, the second negative battery terminal, the second loadterminal, and the source of the first N-channel MOSFET are coupled toeach other.

According to a further aspect, a method of protecting a load from areverse battery connection is provided. The method comprises coupling asource of a first P-channel MOSFET to a first load terminal, coupling asource of a first N-channel MOSFET to a second load terminal, coupling afirst positive battery terminal connector to a drain of the firstP-channel MOSFET and to a gate of the first N-channel MOSFET, the firstpositive battery terminal configured to electrically connect to a firstbattery terminal, and coupling a first negative battery terminalconnector to a drain of the first N-channel MOSFET and to a gate of thefirst P-channel MOSFET, the first negative battery terminal configuredto electrically connect to a second battery terminal.

According to a still further aspect, another method of protecting a loadfrom a reverse battery connection is provided. The method comprisescoupling a gate of a first P-channel MOSFET to a drain of a secondP-channel MOSFET and to a drain of a first N-channel MOSFET, coupling adrain of the first P-channel MOSFET to a first load terminal, coupling asource of the first P-channel MOSFET to a source of the second P-channelMOSFET and to a first positive battery terminal connector, the firstpositive battery terminal connector configured to electrically connectto a first battery terminal, coupling a gate of the second P-channelMOSFET to a gate of the first N-channel MOSFET and to a second positivebattery terminal connector, the second positive battery terminalconnector configured to electrically connect to a second batteryterminal, and coupling a source of the first N-channel MOSFET to a firstnegative battery terminal connector, to a second negative batteryterminal connector, and to a second load terminal; wherein the firstnegative battery terminal connector is configured to electricallyconnect to a third battery terminal, and the second negative batteryterminal connector is configured to electrically connect to a fourthbattery terminal.

Still other aspects, features, and advantages of the invention may bereadily apparent from the following detailed description wherein anumber of example embodiments and implementations are described andillustrated, including the best mode contemplated for carrying out theinvention. The invention may also include other and differentembodiments, and its several details may be modified in variousrespects, all without departing from the scope of the invention.Accordingly, the drawings and descriptions are to be regarded asillustrative in nature, and not as restrictive. The drawings are notnecessarily drawn to scale. The invention covers all modifications,equivalents, and alternatives falling within the scope of the invention.

BRIEF DESCRIPTION OF DRAWINGS

The skilled artisan will understand that the drawings, described below,are for illustration purposes only. The drawings are not intended tolimit the scope of the disclosure in any way.

FIG. 1 illustrates a simplified top schematic view of an examplebiosensor meter powered by a pair of batteries coupled in parallelaccording to the prior art.

FIG. 2 illustrates a cross-sectional side view of a side-contact batteryholder configured to receive a pair of coin or lithium cell batteriescoupled in parallel according to the prior art.

FIG. 3 illustrates a cross-sectional side view of a top-contact batteryholder configured to receive a pair of coin or lithium cell batteriescoupled in parallel according to the prior art.

FIG. 4 illustrates a cross-sectional side view of the side-contactbattery holder of FIG. 2 with a reverse-connected battery.

FIG. 5 illustrates a cross-sectional side view of the top-contactbattery holder of FIG. 3 with a reverse-connected battery.

FIG. 6 illustrates a schematic circuit diagram of a known reversebattery protection circuit according to the prior art.

FIG. 7 illustrates a schematic circuit diagram of a side-contact batterycircuit with a reverse-connected battery according to the prior art.

FIG. 8 illustrates a schematic circuit diagram of a top-contact batterycircuit with a reverse-connected battery according to the prior art.

FIG. 9 illustrates a schematic circuit diagram of a reverse batteryprotection circuit used with a top-contact battery holder according toembodiments.

FIG. 10 illustrates a schematic circuit diagram of the reverse batteryprotection circuit of FIG. 9 used with a top-contact battery holderhaving a reverse-connected battery.

FIG. 11 illustrates a schematic circuit diagram of a reverse batteryprotection circuit used with a side-contact battery holder according toembodiments.

FIG. 12 illustrates a schematic circuit diagram of the reverse batteryprotection circuit of FIG. 11 used with a side-contact battery holderhaving a reverse-connected battery.

FIG. 13 illustrates a flowchart of a method of protecting a load from areverse battery connection according to embodiments.

FIG. 14 illustrates a flowchart of another method of protecting a loadfrom a reverse battery connection according to embodiments.

DETAILED DESCRIPTION

Reference will now be made in detail to the example embodiments of thisdisclosure, which are illustrated in the accompanying drawings. Whereverpossible, the same reference numbers will be used throughout thedrawings to refer to the same or like parts.

In one aspect, the load (e.g., electronics or circuitry) of abattery-powered device can be protected from a reverse batteryconnection by a protection circuit incorporated in the device. Theprotection circuit can include both P-channel and N-channel MOSFETs(metal-oxide-semiconductor-field-effect-transistors), wherein at leastsome of the gates of those P-channel and N-channel MOSFETs can becoupled directly (i.e., with no intervening device(s) or circuitcomponent(s) excluding resistive elements) to the battery terminalconnectors of the device. In some embodiments, each positive batteryterminal connector in a device can be connected to a gate of arespective N-channel MOSFET or to both a gate of a respective P-channelMOSFET and a gate of a respective N-channel MOSFET, depending on thetype of battery connectors used in the device. In some embodiments, eachnegative battery terminal connector in a device can be connected to agate of a respective P-channel MOSFET. In the event of a reverse batteryconnection, at least one P-channel MOSFET and at least one N-channelMOSFET can switch into a non-conductive state (i.e., they each “turnoff”). The switching into non-conductive states can isolate, andtherefore protect, a device's load from an incorrectly installedbattery. The protection circuit can also prevent an incorrectlyinstalled battery, and/or other battery coupled in parallel with theincorrectly installed battery, from prematurely discharging. In otheraspects, methods of protecting a load from a reverse battery connectionare provided, as will be explained in greater detail below in connectionwith FIGS. 1-14.

FIG. 1 illustrates an example of a known device, a biosensor meter 100,powered by batteries coupled in parallel according to the prior art.Biosensor meter 100 can be powered by first and second batteries 102 aand 102 b coupled in parallel and seated in a battery holder 104. Firstand second batteries 102 a and 102 b can be identical and can each be,e.g., a coin or lithium cell type battery, such as, e.g., a 3-voltCR2032 battery. Battery holder 104 can be located in a batterycompartment 106, which can be accessible from the back 107 of biosensormeter 100. Biosensor meter 100 can also include a microcontroller 108and a memory 109 powered by first and second batteries 102 a and 102 b.Microcontroller 108 can be configured to determine a property of ananalyte in a fluid, such as, e.g., a concentration of blood glucose in asample of blood, and memory 109 can be configured to store measurementresults. Microcontroller 108 can be a conventional microcontroller, suchas, e.g., a V850 microcontroller by Renesas Electronics America Inc., ofSanta Clara, Calif., or another similar microcontroller. Othercomponents of biosensor meter 100 can include, e.g., input/outputdevices, a display, and a test sensor port (none shown), all of whichcan be powered by first and second batteries 102 a and 102 b.Microcontroller 108, memory 109, and the other electrical components ofbiosensor meter 100 can be considered the “load” powered by first andsecond batteries 102 a and 102 b. A housing 110 can be configured tohouse therein first and second batteries 102 a and 102 b, battery holder104, battery compartment 106, microcontroller 108, memory 109, and theother components of biosensor meter 100. An example of a biosensor meter100 can be the CONTOUR® USB Blood Glucose Meter by Bayer Healthcare, ofTarrytown, N.Y.

FIGS. 2 and 3 illustrate two known types of battery holders 204 and 304,respectively, that can each be used in, e.g., biosensor meter 100, aswell as in other battery-powered devices requiring parallel-coupledbatteries, according to the prior art. Battery holders 204 and 304 caneach be configured to receive and couple in parallel first and secondbatteries 202 a and 202 b. First and second batteries 202 a and 202 bcan each be identical coin or lithium cell batteries, wherein firstbattery 202 a can have a first positive battery terminal 212 a and afirst negative battery terminal 214 a, and second battery 202 b can havea second positive battery terminal 212 b and a second negative batteryterminal 214 b. First positive battery terminal 212 a and first negativebattery terminal 214 a can each be made of one or more metals and/orother electrically conductive material(s) that together form a housingof first battery 202 a, wherein first positive battery terminal 212 a iselectrically insulated from first negative battery terminal 214 a.Second positive battery terminal 212 b and second negative batteryterminal 214 b can also each be made of one or more metals and/or otherelectrically conductive material(s) that together form a housing ofsecond battery 202 b, wherein second positive battery terminal 212 b iselectrically insulated from second negative battery terminal 214 b.First and second batteries 202 a and 202 b can each be, e.g., a 3-voltCR2032 or similar battery.

As shown in FIG. 2, known battery holder 204 can be configured as aside-contact battery holder, and can include a first battery section 216a and a second battery section 216 b. First and second battery sections216 a and 216 b can be configured identically or as mirror images ofeach other, as shown. First battery section 216 a can be configured toreceive first battery 202 a, and second battery section 216 b can beconfigured to receive second battery 202 b (or vice versa). Firstbattery section 216 a can include a first support structure 218 aconfigured to hold first battery 202 a in place, and second batterysection 216 b can include a second support structure 218 b configured tohold second battery 202 b in place.

Battery holder 204 can include first and second side connectors 220 aand 220 b and first and second bottom connectors 222 a and 222 b. Uponproper installation of first battery 202 a in first support structure218 a, first side connector 220 a can engage and electrically connect toa side 213 a of first positive battery terminal 212 a, and first bottomconnector 222 a can engage and electrically connect to a bottom 215 a offirst negative battery terminal 214 a. Upon proper installation ofsecond battery 202 b in second support structure 218 b, second sideconnector 220 b can engage and electrically connect to a side 213 b ofsecond positive battery terminal 212 b, and second bottom connector 222b can engage and electrically connect to a bottom 215 b of secondnegative battery terminal 214 b.

First and second side connectors 220 a and 220 b can each beelectrically connected to, or integrally formed with, a positivepolarity conductor 224. First and second bottom connectors 222 a and 222b can each be electrically connected to, or integrally formed with, anegative polarity conductor 226. Positive polarity conductor 224 andnegative polarity conductor 226 are electrically isolated from eachother by a base 228 of battery holder 204. Base 228 can be made of anysuitable electrically-insulating material, such as, e.g., any suitableplastic and/or rubber based material. Positive polarity conductor 224and negative polarity conductor 226 can be coupled to respectivepositive and negative load terminals of a device's load.

As shown in FIG. 3, known battery holder 304 can be configured as atop-contact battery holder, and can include a first battery section 316a and a second battery section 316 b. First and second battery sections316 a and 316 b can be configured identically, as shown, or as mirrorimages of each other. First battery section 316 a can be configured toreceive first battery 202 a, and second battery section 316 b can beconfigured to receive second battery 202 b (or vice versa). Firstbattery section 316 a can include a first support structure 318 aconfigured to hold first battery 202 a in place, and second batterysection 316 b can include a second support structure 318 b configured tohold second battery 202 b in place.

Battery holder 304 can include first and second top connectors 320 a and320 b and first and second bottom connectors 322 a and 322 b. Uponproper installation of first battery 202 a in first support structure318 a, first top connector 320 a can engage and electrically connect toa top 317 a of first positive battery terminal 212 a, and first bottomconnector 322 a can engage and electrically connect to a bottom 215 a offirst negative battery terminal 214 a. Upon proper installation ofsecond battery 202 b in second support structure 318 b, second topconnector 320 b can engage and electrically connect to a top 317 b ofsecond positive battery terminal 212 b, and second bottom connector 322b can engage and electrically connect to a bottom 215 b of secondnegative battery terminal 214 b.

First and second top connectors 320 a and 320 b can each be electricallyconnected to, or integrally formed with, a positive polarity conductor324. First and second bottom connectors 322 a and 322 b can each beelectrically connected to, or integrally formed with, a negativepolarity conductor 326. Positive polarity conductor 324 and negativepolarity conductor 326 are electrically isolated from each other by abase 328 of battery holder 304. Base 328 can be made of any suitableelectrically-insulating material, such as, e.g., any suitable plasticand/or rubber based material. Positive polarity conductor 324 andnegative polarity conductor 326 can be coupled to respective positiveand negative load terminals of a device's load.

FIGS. 4 and 5 illustrate the adverse effects of a reverse batteryconnection in known battery holders 204 and 304, respectively.

As shown in FIG. 4, first battery 202 a is improperly installed upsidedown in first battery section 216 a of known battery holder 204. As aresult, first side connector 220 a and first bottom connector 222 a areboth in contact with and electrically connected to first positivebattery terminal 212 a. This reverse battery connection can cause secondbattery 202 b, which is properly installed, to prematurely discharge bycreating a current path (illustrated by arrows) through first positivebattery terminal 212 a and second battery 202 b as follows: current canflow from second positive battery terminal 212 b into second sideconnector 220 b, through positive polarity conductor 224 to first sideconnector 220 a. Improperly installed first battery 202 a, which iselectrically floating (because first negative battery terminal 214 a isnot electrically connected to anything), provides an electricalconnection from first side connector 220 a to first bottom connector 222a. Current can therefore flow from first side connector 220 a into firstbottom connector 222 a, through negative polarity conductor 226 tosecond bottom connector 222 b and into second negative battery terminal214 b of second battery 202 b, completing the discharge circuit. Thesame adverse effect can occur if second battery 202 b is improperlyinstalled instead of first battery 202 a.

Note that improper installation of both first and second batteries 202 aand 202 b in known side-contact battery holder 204 can cause both firstand second batteries 202 a and 202 b to electrical float. Thus, whilenot causing either battery to prematurely discharge, neither battery canprovide any power to a device's load.

Referring now to FIG. 5, first battery 202 a is improperly installedupside down in first battery section 316 a of known battery holder 304.As a result, first top connector 320 a can be in contact with andelectrically connected to first negative battery terminal 214 a, whilefirst bottom connector 322 a can be in contact with and electricallyconnected to first positive battery terminal 212 a. This reverse batteryconnection can create a short circuit that can cause both first battery202 a and second battery 202 b to prematurely discharge. The improperinstallation of first battery 202 a can create a current path(illustrated by arrows) through first and second batteries 202 a and 202b as follows: current flow can from first positive battery terminal 212a of improperly installed first battery 202 a into first bottomconnector 322 a, through negative polarity conductor 326 to secondbottom connector 322 b. Current can flow from second bottom connector322 b through properly installed second battery 202 b via secondnegative battery terminal 214 b and second positive battery terminal 212b into second top connector 320 b. Current can flow from second topconnector 320 b through positive polarity conductor 324 to first topconductor 320 a and into first negative battery terminal 214 a of firstbattery 202 a, completing the short circuit. The same adverse effect canoccur if second battery 202 b is improperly installed instead of firstbattery 202 a.

Note that improper installation of both first and second batteries 202 aand 202 b in known top-contact battery holder 304, while not creating ashort circuit that can prematurely discharge either battery, can cause adevice's load to receive power at reverse polarity, which can damage adevice's load and/or cause abnormal device operation.

FIG. 6 shows a known protection circuit 600 that can be used in a devicepowered by a pair of parallel-coupled first and second batteries 602 aand 602 b in accordance with the prior art. First and second batteries602 a and 602 b can be, e.g., coin or lithium cell batteries, such as,e.g., CR2032 batteries, that can power a device's load 630. Protectioncircuit 600 can include first and second diodes 632 a and 632 b, whichcan each be, e.g., Schottky diodes. Other types of diodes canalternatively be used. First diode 632 a can be coupled in seriesbetween a first positive battery terminal 612 a of battery 602 a and apositive load terminal 634 of protection circuit 600. Second diode 632 bcan be coupled in series between a second positive battery terminal 612b of battery 602 b and positive load terminal 634. A negative loadterminal 636 of protection circuit 600 can be coupled to first andsecond negative battery terminals 614 a and 614 b. Load 630 can becoupled between positive load terminal 634 and negative load terminal636.

In the event of a reverse battery connection (not shown) of, e.g., firstbattery 602 a in either a side-contact battery holder or a top-contactbattery holder such as, e.g., battery holders 204 and 304, respectively,first diode 632 a can become reverse biased and can switch into anon-conductive state. This can isolate (i.e., protect) load 630 fromreverse-connected first battery 602 a and can prevent either firstbattery 602 a and/or second battery 602 b from prematurely discharging.Similarly, in the event second battery 602 b is alternatively oradditionally reverse connected, second diode 632 b can also becomereverse biased and can switch into a non-conductive state, which canisolate (i.e., protect) load 630 from reverse-connected second battery602 b and can prevent first battery 602 a and/or second battery 602 bfrom prematurely discharging. However, in normal device operation whereboth first and second diodes 632 a and 632 b are forward biased (i.e.,in a conductive state), protection circuit 600 may not be efficient atlow battery voltage. For example, assuming first and second diodes 632 aand 632 b each have a forward voltage of about 0.3 volts, and a CR2032battery has a low voltage of about 1.8 volts, power losses can be asmuch as about 17%, which may not be acceptable in many battery-powereddevices.

As is known in the art, MOSFETs have virtually no power loss when in theconductive state and, therefore, MOSFETs are sometimes used instead ofdiodes in devices sensitive to power losses. For example, in deviceshaving a single battery, a P-channel MOSFET may be used instead of adiode to provide reverse battery protection. However, in devices poweredby parallel-coupled batteries, simply replacing diodes, such as firstand second diodes 632 a and 632 b of FIG. 6, with respective P-channelMOSFETs does not provide reverse battery protection, as described belowin connection with FIGS. 7 and 8.

FIG. 7 shows a side-contact battery circuit 700 according to the priorart. Side-contact battery circuit 700 can include parallel-coupled firstand second batteries 702 a and 702 b that together can power a load 730.First and second batteries 702 a and 702 b can each be, e.g., a coin orlithium cell battery. Side-contact battery circuit 700 can also includefirst and second P-channel MOSFETs 732 a and 732 b. First P-channelMOSFET 732 a can be coupled in series between first battery 702 a and apositive load terminal 734 (thus replacing first diode 632 a), andsecond P-channel MOSFET 732 b can be coupled in series between secondbattery 702 b and positive load terminal 734 (thus replacing seconddiode 632 b). Load 730 can be coupled between positive load terminal 734and a negative load terminal 736.

As shown, first battery 702 a is correctly installed and second battery702 b is incorrectly installed (i.e., upside down), resulting in areverse battery connection. This reverse battery installation can resultin both side connector 720 b and bottom connector 722 b contacting andelectrically connecting to positive battery terminal 712 b, which cancause second battery 702 b to electrically float (because negativebattery terminal 714 b is not electrically connected to anything). Thedirect electrical connection from side connector 720 b to bottomconnector 722 b via positive battery terminal 712 b can create a currentpath (illustrated by arrows) that can prematurely discharge firstbattery 702 a, which is correctly installed. As shown, current can flowfrom positive terminal 712 a of first battery 702 a through first andsecond P-channel MOSFETs 732 a and 732 b, which are both in a conductivestate (i.e., they are both “on”) because a voltage at their respectivegates (designated “G”) is sufficiently low relative to a voltage attheir respective sources (designated “5”). Current can therefore flowthrough second P-channel MOSFET 732 b into side connector 720 b and outbottom connector 722 b via positive battery terminal 712 b, and intonegative battery terminal 714 a of first battery 702 a, completing thedischarge circuit. No current (or negligible current) is likely to flowinto load 730, because the resistance through second P-channel MOSFET732 b and second battery 702 b to negative battery terminal 714 a isnegligible, thus drawing all or substantially all of the currentreceived at positive load terminal 734 away from load 730. The sameadverse effect can occur if first battery 702 a is improperly installedinstead of second battery 702 b. Accordingly, replacing diodes withP-channel MOSFETs as shown in side-contact battery circuit 700 does notprevent premature battery discharge in the event of a reverse batteryconnection.

FIG. 8 shows a top-contact battery circuit 800 according to the priorart. Top-contact battery circuit 800 can include parallel-coupled firstand second batteries 802 a and 802 b that together can power a load 830.First and second batteries 802 a and 802 b can each be, e.g., a coin orlithium cell battery. Top-contact battery circuit 800 can also includefirst and second P-channel MOSFETs 832 a and 832 b. First P-channelMOSFET 832 a can be coupled in series between first battery 702 a and apositive load terminal 834 (thus replacing first diode 632 a), andsecond P-channel MOSFET 832 b can be coupled in series between secondbattery 802 b and positive load terminal 834 (thus replacing seconddiode 632 b). Load 830 can be coupled between positive load terminal 834and a negative load terminal 836.

As shown, first battery 802 a is correctly installed and second battery802 b is incorrectly installed (i.e., upside down), resulting in areverse battery connection. This reverse battery installation can causetop connector 820 b to contact and electrically connect to negativebattery terminal 814 b, while bottom connector 822 b contacts andelectrically connects to positive battery terminal 812 b, instead ofvice-versa when second battery 802 b is correctly installed. Thisreverse battery connection results in a current path (illustrated byarrows) that can prematurely discharge both first and second batteries802 a and 802 b. As shown, current can flow from positive terminal 812 aof first battery 802 a through first and second P-channel MOSFETs 832 aand 832 b, which are both in a conductive state (i.e., they are both“on”) because a voltage at their respective gates (designated “G”) issufficiently low relative to a voltage at their respective sources(designated “S”). Current can therefore flow through second P-channelMOSFET 832 b and reverse-connected second battery 802 b and intonegative battery terminal 814 a of first battery 802 a, completing thedischarge circuit. A small amount of current received at positive loadterminal 834 may flow into load 830, because the resistance throughsecond battery 802 b may not be negligible. However, that small amountof current is not likely to be sufficient to properly and/or fully driveload 830. The same adverse effect can occur if first battery 802 a isimproperly installed instead of second battery 802 b. Accordingly,replacing diodes with P-channel MOSFETs as shown in top-contact batterycircuit 800 does not prevent premature battery discharge in the event ofa reverse battery connection.

FIG. 9 shows a battery protection circuit 900 in accordance with one ormore embodiments. Battery protection circuit 900 can protect a device'sload 903 and/or prevent parallel-coupled first and second batteries 902a and 902 b, which can be coin or lithium cell batteries, fromprematurely discharging in the event of a reverse battery connection. Insome embodiments, battery protection circuit 900 can be incorporated in,e.g., biosensor meter 100, and/or other suitable devices having atop-contact battery holder such as, e.g., battery holder 304. In someembodiments, battery protection circuit 900 can be integrated with adevice's load circuitry or, alternatively, integrated with a batteryholder incorporated in a battery-powered device. In other embodiments,battery protection circuit 900 can be incorporated in a device as adiscrete circuit (e.g., in the form of an integrated circuit chip and/ormodule) coupled between a top-contact battery holder and a load. Batteryprotection circuit 900 can alternatively be incorporated in a device inother suitable ways.

As shown in FIG. 9, battery protection circuit 900 can in someembodiments include a pair of battery protection cells 940 a and 940 b,which can be identical to each other. Battery protection cell 940 a caninclude a first P-channel MOSFET 932 a and a first N-channel MOSFET 933a, each of which can be an enhancement-mode type MOSFET in someembodiments. In other embodiments, first MOSFETs 932 a and 933 a caneach be other suitable types of FETs (field effect transistors). Thesource (designated “S”) of first P-channel MOSFET 932 a can be coupledto a positive load terminal 934, and the source of first N-channelMOSFET 933 a can be coupled to a negative load terminal 936. Load 930can be coupled between positive load terminal 934 and negative loadterminal 936. The drain (designated “D”) of first P-channel MOSFET 932 acan be coupled to a positive battery terminal connector 942 a and to thegate (designated “G”) of first N-channel MOSFET 933 a. The drain offirst N-channel MOSFET 933 a can be coupled to a negative batteryterminal connector 944 a and to the gate of first P-channel MOSFET 932a. In some embodiments, resistive elements (e.g., resistors) canoptionally be coupled in series between a battery terminal and a MOSFETgate to protect against electrostatic discharge (ESD). For example, insome embodiments, resistor 938 a can be coupled between the gate offirst N-channel MOSFET 933 a and positive battery terminal connector 942a, and resistor 939 a can be coupled between the gate of first P-channelMOSFET 932 a and negative battery terminal connector 944 a. In someembodiments, values for resistors 938 a and 939 a can range from about10 k ohms to about 3 M ohms.

In some embodiments, positive battery terminal connector 942 a can beelectrically connected to a top connector 920 a of battery holder 904,while negative battery terminal connector 944 a can be electricallyconnected to bottom connector 922 a of battery holder 904. In otherembodiments, positive battery terminal connector 942 a can be integrallyformed with top connector 920 a of battery holder 904, while negativebattery terminal connector 944 a can be integrally formed with bottomconnector 922 a of battery holder 904.

Battery protection cell 940 b, which in this embodiment is configuredidentically as battery protection cell 940 a, can include a secondP-channel MOSFET 932 b and a second N-channel MOSFET 933 b, each ofwhich can be an enhancement-mode type MOSFET in some embodiments. Inother embodiments, MOSFETs 932 b and 933 b can each be other suitabletypes of FETs. The source (designated “S”) of second P-channel MOSFET932 b can be coupled to positive load terminal 934, and the source ofsecond N-channel MOSFET 933 b can be coupled to negative load terminal936. The drain (designated “D”) of second P-channel MOSFET 932 b can becoupled to a positive battery terminal connector 942 b and to the gate(designated “G”) of second N-channel MOSFET 933 b. The drain of secondN-channel MOSFET 933 b can be coupled to a negative battery terminalconnector 944 b and to the gate of second P-channel MOSFET 932 b. Insome embodiments, resistor 938 b can optionally be coupled between thegate of second N-channel MOSFET 933 b and positive battery terminalconnector 942 b, and resistor 939 b can be coupled between the gate ofsecond P-channel MOSFET 932 b and negative battery terminal connector944 b. Resistors 938 b and 939 b can be used to protect against ESD. Insome embodiments, values for resistors 938 b and 939 b can range fromabout 10 k ohms to about 3M ohms.

In some embodiments, positive battery terminal connector 942 b can beelectrically connected to a top connector 920 b of battery holder 904,while negative battery terminal connector 944 b can be electricallyconnected to bottom connector 922 b of battery holder 904. In otherembodiments, positive battery terminal connector 942 b can be integrallyformed with top connector 920 b of battery holder 904, while negativebattery terminal connector 944 b can be integrally formed with bottomconnector 922 b of battery holder 904.

In alternative embodiments, battery protection circuit 900 can includeonly one or more than two battery protection cells 940 a and/or 940 bdepending on the number of parallel-coupled batteries in the device. Forexample, in devices having more than two parallel-coupled batteries, arespective battery protection cell 940 a or 940 b can be coupled to eachparallel-coupled battery to provide protection against a reverse batteryconnection. In devices having only a single battery, one of batteryprotection cells 940 a or 940 b can be coupled to that battery toprovide protection against a reverse battery connection. Furthermore, indevices utilizing other (e.g., non-battery) sources of power, a singlebattery protection cell 940 a or 940 b can be used to provide protectionagainst a reverse polarity power connection.

In normal operation, first and second batteries 902 a and 902 b areproperly installed as shown in FIG. 9. That is, first positive batteryterminal connector 942 a is electrically coupled to positive batteryterminal 912 a, first negative battery terminal connector 944 a iselectrically coupled to negative battery terminal 914 a, second positivebattery terminal connector 942 b is electrically coupled to positivebattery terminal 912 b, and second negative battery terminal connector944 b is electrically coupled to negative battery terminal 914 b. Firstand second P-channel MOSFETs 932 a and 932 b can both be in a conductivestate (i.e., they are “on”), because a voltage at their respective gatesis sufficiently low relative to a voltage at their respective sources.First and second N-channel MOSFETS 933 a and 933 b can also both be in aconductive state (i.e., they are “on”), because a voltage at theirrespective gates is sufficiently high relative to a voltage at theirrespective sources. Current can therefore flow from first and secondbatteries 902 a and 902 b through respective first and second P-channelMOSFETs 932 a and 932 b to positive load terminal 934 and into load 930.

In the event of a reverse battery connection wherein, e.g., secondbattery 902 b is incorrectly installed (e.g., upside down in the case ofa coin or lithium cell battery), as shown in FIG. 10, positive batteryterminal connector 942 b can be electrically coupled to negative batteryterminal 914 b, and negative battery terminal connector 944 b can beelectrically coupled to positive battery terminal 912 b. This reversebattery connection can cause second P-channel MOSFET 932 b to switchinto a non-conductive state (i.e., to turn “off”), because the voltageat the gate of second P-channel MOSFET 932 b, which is received frompositive voltage terminal 912 b of second battery 902 b, is no longersufficiently low to keep second P-channel MOSFET 932 b on, but isinstead high relative to the voltage at the source of second P-channelMOSFET 932 b. This reverse battery connection also can cause secondN-channel MOSFET 933 b to switch into a non-conductive state (i.e., toturn “off”), because the voltage at the gate of second N-channel MOSFET933 b, which is received from negative voltage terminal 914 b of secondbattery 902 b, is no longer sufficiently high to keep second N-channelMOSFET 933 b on, but is instead low relative to the voltage at thesource of second N-channel MOSFET 933 b. With both second P-channelMOSFET 932 b and second N-channel MOSFET 933 b turned off, load 930 cantherefore be protected (i.e., isolated) from reverse-connected secondbattery 902 b, while first battery 902 a can continue to provide powerto load 930, albeit not necessarily enough for load 930 to properlyoperate. Furthermore, neither first battery 902 a nor second battery 902b is subject to premature discharge as a result of a reverse batteryconnection.

In the event that first battery 902 a is incorrectly installed insteadof second battery 902 b, battery protection cell 940 a can provide thesame load and premature battery discharge protection as batteryprotection cell 940 b described above. And in the event that both firstand second batteries 902 a and 902 b are incorrectly installed, bothbattery protection cells 940 a and 940 b can operate to isolate load 930and prevent premature battery discharge as described above for batteryprotection cell 940 b.

Although described above in connection with coin or lithium cellbatteries, battery protection circuit 900 can be used in devices poweredby other types of suitable batteries where incorrect batteryinstallation can result in a reverse polarity connection (i.e., apositive battery terminal connector electrically coupled to a negativebattery terminal and a negative battery terminal connector electricallycoupled to a positive battery connector).

FIG. 11 shows another battery protection circuit 1100 in accordance withone or more embodiments. Battery protection circuit 1100 can protect adevice's load 1130 and prevent one or both parallel-coupled first andsecond batteries 1102 a and 1102 b from prematurely discharging in theevent of a reverse battery connection. In some embodiments, batteryprotection circuit 1100 can be incorporated in, e.g., biosensor meter100, and/or other suitable devices having a side-contact battery holdersuch as, e.g., battery holder 204. In some embodiments, batteryprotection circuit 1100 can be integrated with a device's load circuitryor, alternatively, integrated with a battery holder incorporated in abattery-powered device. In other embodiments, battery protection circuit1100 can be incorporated in a device as a discrete circuit (e.g., in theform of an integrated circuit chip and/or module) coupled between aside-contact battery holder and a load. Battery protection circuit 1100can alternatively be incorporated in a device in other suitable ways.

As shown in FIG. 11, battery protection circuit 1100 can include a firstP-channel MOSFET 1132 a, a second P-channel MOSFET 1146 a, and a firstN-channel MOSFET 1133 a, each of which can be an enhancement-mode typeMOSFET in some embodiments. In other embodiments, MOSFETs 1132 a, 1146a, and 1133 a can each be other suitable types of FETs. The drain(designated “D”) of first P-channel MOSFET 1132 a can be coupled to apositive load terminal 1134, and the source (designated “S”) of firstN-channel MOSFET 1133 a can be coupled to a negative load terminal 1136.Load 1130 can be coupled between positive load terminal 1134 andnegative load terminal 1136. The gate (designated “G”) of firstP-channel MOSFET 1132 a can be coupled to the drain of second P-channelMOSFET 1146 a and to the drain of first N-channel MOSFET 1133 a. Thesource of first P-channel MOSFET 1132 a can be coupled to the source ofsecond P-channel MOSFET 1146 a and to a first positive battery terminalconnector 1142 a. First positive battery terminal connector 1142 a canbe electrically connected to a side connector 1120 a or, in alternativeembodiments, integrally formed with side connector 1120 a. The gate ofsecond P-channel MOSFET 1146 a can be coupled to the gate of firstN-channel MOSFET 1133 a and to a second positive battery terminalconnector 1142 b. Second positive battery terminal connector 1142 b canbe electrically connected to a side connector 1120 b or, in alternativeembodiments, integrally formed with side connector 1120 b. The source offirst N-channel MOSFET 1133 a can be coupled to a first negative batteryterminal connector 1144 a. First negative battery terminal connector1144 a can be electrically connected to a bottom connector 1122 a or, inalternative embodiments, integrally formed with bottom connector 1122 a.

Battery protection circuit 1100 can also include a third P-channelMOSFET 1132 b, a fourth P-channel MOSFET 1146 b, and a second N-channelMOSFET 1133 b, each of which can be an enhancement-mode type MOSFET insome embodiments. In other embodiments, MOSFETs 1132 b, 1146 b, and 1133b can each be other suitable types of FETs. The drain (designated “D”)of third P-channel MOSFET 1132 b can be coupled to positive loadterminal 1134, and the source (designated “5”) of second N-channelMOSFET 1133 b can be coupled to negative load terminal 1136. The gate(designated “G”) of third P-channel MOSFET 1132 b can be coupled to thedrain of fourth P-channel MOSFET 1146 b and to the drain of secondN-channel MOSFET 1133 b. The source of third P-channel MOSFET 1132 b canbe coupled to the source of fourth P-channel MOSFET 1146 b and to secondpositive battery terminal connector 1142 b. The gate of fourth P-channelMOSFET 1146 b can be coupled to the gate of second N-channel MOSFET 1133b and to first positive battery terminal connector 1142 a. The source ofsecond N-channel MOSFET 1133 b can be coupled to a second negativebattery terminal connector 1144 b. Second negative battery terminalconnector 1144 b can be electrically connected to a bottom connector1122 b or, in alternative embodiments, integrally formed with bottomconnector 1122 b.

In some embodiments of battery protection circuit 1100, resistors canoptionally be coupled in series to the MOSFET gates to protect againstelectrostatic discharge (ESD). For example, in some embodiments,resistor 1138 a can be coupled between the gate of first P-channelMOSFET 1132 a and the drains of second P-channel MOSFET 1146 a and firstN-channel MOSFET 1133 a. Resistor 1139 a can be coupled between firstpositive battery terminal connector 1142 a to the gates of fourthP-channel MOSFET 1146 b and second N-channel MOSFET 1133 b. Resistor1138 b can be coupled between the gate of third P-channel MOSFET 1132 band the drains of fourth P-channel MOSFET 1146 b and second N-channelMOSFET 1133 b. Resistor 1139 b can be coupled between second positivebattery terminal connector 1142 b to the gates of second P-channelMOSFET 1146 a and first N-channel MOSFET 1133 a. In some embodiments,values for resistors 1138 a, 1138 b, 1139 a, and 1139 b can range fromabout 10 k ohms to about 3 M ohms.

In normal operation, first and second batteries 1102 a and 1102 b areproperly installed as shown in FIG. 11. That is, first positive batteryterminal connector 1142 a can be electrically coupled to positivebattery terminal 1112 a, first negative battery terminal connector 1144a can be electrically coupled to negative battery terminal 1114 a,second positive battery terminal connector 1142 b can be electricallycoupled to positive battery terminal 1112 b, and second negative batteryterminal connector 1144 b can be electrically coupled to negativebattery terminal 1114 b. As a result, both second and fourth P-channelMOSFETs 1146 a and 1146 b can be in a non-conductive state (i.e., theyare “off”), because a voltage at their respective gates received fromsecond positive battery terminal 1112 b and first positive batteryterminal 1112 a, respectively, is not sufficiently low relative to avoltage at their respective sources to turn on the second and fourthP-channel MOSFETs 1146 a and 1146 b. Both first and second N-channelMOSFETS 1133 a and 1133 b can be in a conductive state (i.e., they are“on”), because a voltage at their respective gates also received fromsecond positive battery terminal 1112 b and first positive batteryterminal 1112 a, respectively, is sufficiently high relative to avoltage at their respective sources. This can allow both first and thirdP-channel MOSFETs 1132 a and 1132 b to be in a conductive state (i.e.,they are “on”), because a voltage at their respective gates issufficiently low relative to a voltage at their respective sources.Current can therefore flow from first and second batteries 1102 a and1102 b through respective first and third P-channel MOSFETs 1132 a and1132 b to positive load terminal 1134 and into load 1130.

In the event of a reverse battery connection wherein, e.g., secondbattery 1102 b is incorrectly installed (e.g., upside down in the caseof a coin or lithium cell battery), as shown in FIG. 12, second positivebattery terminal connector 1142 b and second negative battery terminalconnector 1144 b can both be electrically coupled to second positivebattery terminal 1112 b. This incorrect installation of second battery1102 b can cause second battery 1102 b to electrically float, becausesecond negative battery terminal 1114 b is not electrically connected toany part of battery protection circuit 1100. Therefore, incorrectlyinstalled second battery 1102 b can provide no power and serves only toconnect together second positive battery terminal connector 1142 b andsecond negative battery terminal connector 1144 b.

As a result, second P-channel MOSFET 1146 a can turn on, because avoltage at the gate of second P-channel MOSFET 1146 a received fromfirst negative battery terminal 1114 a is sufficiently low relative to avoltage at the source of second P-channel MOSFET 1146 a to cause secondP-channel MOSFET 1146 a to switch into a conductive state. FirstN-channel MOSFET 1133 a can turn off, because its gate voltage is alsoreceived from first negative battery terminal 1114 a, which is notsufficiently high relative to a voltage at the source of first N-channelMOSFET 1133 a to keep on first N-channel MOSFET 1133 a. With firstN-channel MOSFET 1133 a turned off, first P-channel MOSFET 1132 a canalso turn off, because its gate voltage is high (via turned on secondP-channel MOSFET 1146 a and first positive battery terminal 1112 a) andis no longer sufficiently low relative to its source voltage to remainin a conductive state. Because the source of third P-channel MOSFET 1132b is now electrically coupled to first negative battery terminal 1114 avia the connection between second positive battery terminal connector1142 b and second negative battery terminal connector 1144 b, thirdP-channel MOSFET 1132 b can also turn off, because its gate voltage isalso no longer sufficiently low relative to its source voltage to remainin a conductive state. Fourth P-channel MOSFET 1146 b can remain off,because a voltage at the gate of fourth P-channel MOSFET 1146 b cancontinue to be received from first positive battery terminal 1112 a.Similarly, the voltage at the gate of second N-channel MOSFET 1133 b cancontinue to be high via first positive battery terminal 1112 a. However,because battery 1102 b provides no power via its incorrect installation,the conductive states of third P-channel MOSFET 1132 b, fourth P-channelMOSFET 1146 b, and second N-channel MOSFET 1133 b can be irrelevant andall can be considered to be in a non-conductive state. Thus, with firstand third P-channel MOSFETs 1132 a and 1132 b turned off, load 1130 cantherefore be protected (i.e., isolated) from incorrectly installedsecond battery 1102 b, and correctly-installed first battery 1102 acannot prematurely discharge, because there is no discharge current paththrough battery protection circuit 1100.

In the event that first battery 1102 a is incorrectly installed insteadof second battery 1102 b, battery protection circuit 1100 can operatesubstantially identically as described above to protect load 1130 andprevent premature battery discharge, except that second P-channel MOSFET1146 a would be off and fourth P-channel MOSFET 1146 b would be on.

FIG. 13 illustrates a method 1300 of protecting a load from a reversebattery connection in accordance with one or more embodiments. Method1300 can be used in connection with devices powered by a single batteryor power source, and/or two or more batteries coupled in parallel,installed in a top-contact battery holder, such as, e.g., battery holder304 of FIG. 3. At process block 1302, method 1300 can include coupling asource of a first P-channel MOSFET to a first load terminal. Forexample, referring to FIG. 9, the source of first P-channel MOSFET 932 acan be coupled to positive load terminal 934.

At process block 1304, method 1300 can include coupling a source of afirst N-channel MOSFET to a second load terminal. Again referring toFIG. 9, e.g., the source of first N-channel MOSFET 933 a can be coupledto negative load terminal 936.

At process block 1306, a first positive battery terminal connector canbe coupled to a drain of the first P-channel MOSFET and to a gate of thefirst N-channel MOSFET. For example, first positive battery terminalconnector 942 a can be coupled to a drain of first P-channel MOSFET 932a and to a gate of first N-channel MOSFET 933 a, as shown in FIG. 9. Insome embodiments, process block 1306 can optionally include coupling aresistive element between the first positive battery terminal connectorand the gate of the first N-channel MOSFET, such as, e.g., couplingresistor 938 a between first positive battery terminal connector 942 aand the gate of first N-channel MOSFET 933 a, to provide protectionagainst ESD.

At process block 1308, method 1300 can include coupling a first negativebattery terminal connector to a drain of the first N-channel MOSFET andto a gate of the first P-channel MOSFET. For example, as shown in FIG.9, first negative battery terminal connector 944 a can be coupled to adrain of first N-channel MOSFET 933 a and to a gate of first P-channelMOSFET 932 a. In some embodiments, process block 1308 can optionallyinclude coupling a resistive element between the first negative batteryterminal connector and the gate of the first P-channel MOSFET, such as,e.g., coupling resistor 939 a between first negative battery terminalconnector 944 a and the gate of first P-channel MOSFET 932 a, to provideprotection against ESD.

FIG. 14 illustrates another method 1400 of protecting a load from areverse battery connection in accordance with one or more embodiments.Method 1400 can be used in connection with devices powered by twoparallel-coupled batteries installed in a side-contact battery holder,such as, e.g., battery holder 204 of FIG. 2. At process block 1402,method 1400 can include coupling a gate of a first P-channel MOSFET to adrain of a second P-channel MOSFET and to a drain of a first N-channelMOSFET. For example, referring to FIG. 11, the gate of first P-channelMOSFET 1132 a can be coupled to the drain of second P-channel MOSFET1146 a and to the drain of first N-channel MOSFET 1133 a.

At process block 1404, method 1400 can include coupling a drain of thefirst P-channel MOSFET to a first load terminal. Again referring to FIG.11, e.g., a drain of first P-channel MOSFET 1132 a can be coupled to apositive load terminal 1134.

At process block 1406, a source of the first P-channel MOSFET can becoupled to a source of the second P-channel MOSFET and to a firstpositive battery terminal connector. For example, a source of firstP-channel MOSFET 1132 a can be coupled to a source of second P-channelMOSFET 1146 a and to first positive battery terminal connector 1142 a,as shown in FIG. 11.

At process block 1408, a gate of the second P-channel MOSFET can becoupled to a gate of the first N-channel MOSFET and to a second positivebattery terminal connector. As also shown in FIG. 11, e.g., a gate ofsecond P-channel MOSFET 1146 a can be coupled to a gate of firstN-channel MOSFET 1133 a and to a second positive battery terminalconnector 1142 b.

At process block 1410, method 1400 can include coupling a source of thefirst N-channel MOSFET to a first negative battery terminal connector,to a second negative battery terminal connector, and to a second loadterminal. For example, again referring to FIG. 11, a source of firstN-channel MOSFET 1133 a can be coupled to first negative batteryterminal connector 1144 a, to second negative battery terminal connector1144 b, and to second load terminal 1136.

The above process blocks of method 1300 and/or method 1400 can beexecuted or performed in an order or sequence not limited to the orderand sequence shown and described. For example, in some embodiments,process blocks 1302, 1304, 1306, and 1308 and/or process blocks 1402,1404, 1406, 1408, and 1410 can performed substantially simultaneously aspart of an integrated circuit fabrication process.

Persons skilled in the art should readily appreciate that the inventiondescribed herein is susceptible of broad utility and application. Manyembodiments and adaptations of the invention other than those describedherein, as well as many variations, modifications, and equivalentarrangements, will be apparent from, or reasonably suggested by, theinvention and the foregoing description thereof, without departing fromthe substance or scope of the invention. For example, although describedin connection with a battery-powered biosensor meter and coin typebatteries, one or more embodiments of the invention may be used withother types of batteries and other types of devices powered by batteriescoupled in parallel and sensitive to battery polarity. Accordingly,while the invention has been described herein in detail in relation tospecific embodiments, it should be understood that this disclosure isonly illustrative and presents examples of the invention and is mademerely for purposes of providing a full and enabling disclosure of theinvention. This disclosure is not intended to limit the invention to theparticular apparatus, devices, assemblies, systems or methods disclosed,but, to the contrary, the intention is to cover all modifications,equivalents, and alternatives falling within the scope of the invention.

What is claimed is:
 1. A reverse battery protection circuit comprising:a first load terminal; a second load terminal; a first P-channel MOSFEThaving a drain, a gate, and a source coupled to the first load terminal;a first N-channel MOSFET having a drain, a gate, and a source coupled tothe second load terminal; a first positive battery terminal connectorcoupled to the drain of the first P-channel MOSFET and to the gate ofthe first N-channel MOSFET, the first positive battery terminalconnector configured to electrically connect to a first batteryterminal; and a first negative battery terminal connector coupled to thedrain of the first N-channel MOSFET and to the gate of the firstP-channel MOSFET, the first negative battery terminal connectorconfigured to electrically connect to a second battery terminal.
 2. Thereverse battery protection circuit of claim 1 wherein the first positivebattery terminal connector has a top contact configuration.
 3. Thereverse battery protection circuit of claim 1 further comprising: afirst resistive element coupled in series between the first positivebattery terminal connector and the gate of the first N-channel MOSFET;and a second resistive element coupled in series between the firstnegative battery terminal connector and the gate of the first P-channelMOSFET.
 4. The reverse battery protection circuit of claim 1 furthercomprising: a second P-channel MOSFET having a drain, a gate, and asource coupled to the first load terminal; a second N-channel MOSFEThaving a drain, a gate, and a source coupled to the second loadterminal; a second positive battery terminal connector coupled to thedrain of the second P-channel MOSFET and to the gate of the secondN-channel MOSFET, the second positive battery terminal connectorconfigured to electrically connect to a third battery terminal; and asecond negative battery terminal connector coupled to the drain of thesecond N-channel MOSFET and to the gate of the second P-channel MOSFET,the second negative battery terminal connector configured toelectrically connect to a fourth battery terminal.
 5. The reversebattery protection circuit of claim 4 wherein the second positivebattery terminal connector has a top contact configuration.
 6. Thereverse battery protection circuit of claim 4 further comprising: athird resistive element coupled in series between the second positivebattery terminal connector and the gate of the second N-channel MOSFET;and a fourth resistive element coupled in series between the firstnegative battery terminal connector and the gate of the second P-channelMOSFET.
 7. The reverse battery protection circuit of claim 4 wherein:the first positive battery terminal connector and the first negativebattery terminal connector are configured to electrically connect torespective battery terminals of a first battery; and the second positivebattery terminal connector and the second negative battery terminalconnector are configured to electrically connect to respective batteryterminals of a second battery.
 8. A battery-powered biosensor metercomprising: a microcontroller configured to determine a property of ananalyte in a fluid; a memory coupled to the microcontroller to storemeasurement results; a battery holder configured to receive a pluralityof batteries; the reverse battery protection circuit of claim 1 coupledto the battery holder, the microcontroller, and the memory; and ahousing configured to house the microcontroller, the memory, the batteryholder, and the reverse battery protection circuit of claim
 1. 9. Areverse battery protection circuit comprising: a first P-channel MOSFEThaving a gate, a drain, and a source; a second P-channel MOSFET having agate, a drain coupled to the gate of the first P-channel MOSFET, and asource coupled to the source of the first P-channel MOSFET; a firstN-channel MOSFET having a gate coupled to the gate of the secondP-channel MOSFET, a drain coupled to the drain of the second P-channelMOSFET and to the gate of the first P-channel MOSFET, and a source; afirst load terminal coupled to the drain of the first P-channel MOSFET;a first positive battery terminal connector coupled to the source of thefirst P-channel MOSFET and to the source of the second P-channel MOSFET,the first positive battery terminal connector configured to electricallyconnect to a first battery terminal; a second positive battery terminalconnector coupled to the gate of the first N-channel MOSFET and to thegate of the second P-channel MOSFET, the second positive batteryterminal connector configured to electrically connect to a secondbattery terminal; a first negative battery terminal connector configuredto electrically connect to a third battery terminal; a second negativebattery terminal connector configured to electrically connect to afourth battery terminal; and a second load terminal; wherein: the firstnegative battery terminal, the second negative battery terminal, thesecond load terminal, and the source of the first N-channel MOSFET arecoupled to each other.
 10. The reverse battery protection circuit ofclaim 9 further comprising: a third P-channel MOSFET having a gate, adrain coupled to the first load terminal and to the drain of the firstP-channel MOSFET, and a source coupled to the second positive batteryterminal connector; a fourth P-channel MOSFET having a gate coupled tothe first positive battery terminal connector, a drain coupled to thegate of the third P-channel MOSFET, and a source coupled to the sourceof the third P-channel MOSFET and to the second positive batteryterminal connector; and a second N-channel MOSFET having a gate coupledto the gate of the fourth P-channel MOSFET and to the first positivebattery terminal connector, a drain coupled to the drain of the fourthP-channel MOSFET and to the gate of the third P-channel MOSFET, and asource coupled to the first negative battery terminal, to the secondnegative battery terminal, to the second load terminal, and to thesource of the first N-channel MOSFET.
 11. The reverse battery protectioncircuit of claim 10 wherein: the first positive battery terminalconnector and the first negative battery terminal connector areconfigured to electrically connect to respective battery terminals of afirst battery; and the second positive battery terminal connector andthe second negative battery terminal connector are configured toelectrically connect to respective battery terminals of a secondbattery.
 12. The reverse battery protection circuit of claim 10 whereinthe first positive battery terminal connector has a side contactconfiguration; and the second positive battery terminal connector has aside contact configuration.
 13. A battery-powered biosensor metercomprising: a microcontroller configured to determine a property of ananalyte in a fluid; a memory coupled to the microcontroller to storemeasurement results; a battery holder configured to receive a pluralityof batteries; the reverse battery protection circuit of claim 10 coupledto the battery holder, the microcontroller, and the memory; and ahousing configured to house the microcontroller, the memory, the batteryholder, and the reverse battery protection circuit of claim
 10. 14. Amethod of protecting a load from a reverse battery connection, themethod comprising: coupling a source of a first P-channel MOSFET to afirst load terminal; coupling a source of a first N-channel MOSFET to asecond load terminal; coupling a first positive battery terminalconnector to a drain of the first P-channel MOSFET and to a gate of thefirst N-channel MOSFET, the first positive battery terminal configuredto electrically connect to a first battery terminal; and coupling afirst negative battery terminal connector to a drain of the firstN-channel MOSFET and to a gate of the first P-channel MOSFET, the firstnegative battery terminal configured to electrically connect to a secondbattery terminal.
 15. The method of claim 14 further comprising:coupling a source of a second P-channel MOSFET to the first loadterminal; coupling a source of a second N-channel MOSFET to the secondload terminal; coupling a second positive battery terminal connector toa drain of the second P-channel MOSFET and to a gate of the secondN-channel MOSFET, the second positive battery terminal connectorconfigured to electrically connect to a third battery terminal; andcoupling a second negative battery terminal connector to a drain of thesecond N-channel MOSFET and to a gate of the second P-channel MOSFET,the second negative battery terminal connector configured toelectrically connect to a fourth battery terminal.
 16. The method ofclaim 14 further comprising providing a battery holder configured toreceive the first positive battery terminal connector and the firstnegative battery connector, wherein the first positive battery terminalconnector has a top contact configuration.
 17. A method of protecting aload from a reverse battery connection, the method comprising: couplinga gate of a first P-channel MOSFET to a drain of a second P-channelMOSFET and to a drain of a first N-channel MOSFET; coupling a drain ofthe first P-channel MOSFET to a first load terminal; coupling a sourceof the first P-channel MOSFET to a source of the second P-channel MOSFETand to a first positive battery terminal connector, the first positivebattery terminal connector configured to electrically connect to a firstbattery terminal; coupling a gate of the second P-channel MOSFET to agate of the first N-channel MOSFET and to a second positive batteryterminal connector, the second positive battery terminal connectorconfigured to electrically connect to a second battery terminal; andcoupling a source of the first N-channel MOSFET to a first negativebattery terminal connector, to a second negative battery terminalconnector, and to a second load terminal; wherein: the first negativebattery terminal connector is configured to electrically connect to athird battery terminal; and the second negative battery terminalconnector is configured to electrically connect to a fourth batteryterminal.
 18. The method of claim 17 further comprising: coupling adrain of a third P-channel MOSFET to the first load terminal and to thedrain of the first P-channel MOSFET; coupling a source of the thirdP-channel MOSFET to the second positive battery terminal connector andto a source of a fourth P-channel MOSFET; coupling a gate of the thirdP-channel MOSFET to a drain of the fourth P-channel MOSFET and to adrain of a second N-channel MOSFET; coupling a gate of the fourthP-channel MOSFET to the first positive battery terminal connector and toa gate of the second N-channel MOSFET; and coupling a source of thesecond N-channel MOSFET to the first negative battery terminal, to thesecond negative battery terminal, to the second load terminal, and tothe source of the first N-channel MOSFET.
 19. The method of claim 17further comprising providing a battery holder for receiving the firstpositive battery terminal connector and the first negative batteryconnector, wherein the first positive battery terminal connector has aside contact configuration.
 20. The method of claim 17 furthercomprising coupling a microcontroller configured to determine a propertyof an analyte in a fluid to the first and second load terminals.